81351666 has 48 divisors (see below), whose sum is σ = 194201280. Its totient is φ = 24406560.

The previous prime is 81351649. The next prime is 81351671. The reversal of 81351666 is 66615318.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 81351666.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 18400 + ... + 22388.

It is an arithmetic number, because the mean of its divisors is an integer number (4045860).

Almost surely, 2^81351666 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81351666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (97100640).

81351666 is an abundant number, since it is smaller than the sum of its proper divisors (112849614).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81351666 is a wasteful number, since it uses less digits than its factorization.

81351666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4111 (or 4108 counting only the distinct ones).

The product of its digits is 25920, while the sum is 36.

The square root of 81351666 is about 9019.5158406646. The cubic root of 81351666 is about 433.3001277646.

It can be divided in two parts, 8135 and 1666, that added together give a square (9801 = 99²).

The spelling of 81351666 in words is "eighty-one million, three hundred fifty-one thousand, six hundred sixty-six".